The present invention relates to pumps and pumping systems and, in particular, to a pump apparatus which self-primes in its active mode and causes variations in the pressure of the pumped fluid to be damped in its passive mode.
Fluid pumps are typically based upon the use of a rotating or reciprocating device such as an impeller which is bearing mounted and driven by some motive means such as an electric motor. Such mechanical pumps, while reasonably efficient, experience wear of the moving parts and are accompanied by significant levels of audible noise.
In order to solve the problems of wear, a pump having essentially no moving parts was developed and is disclosed in my U.S. Pat. No. 3,898,017, issued Aug. 5, 1975. In that patent, a heater ribbon is placed in a chamber containing the pumped fluid. With pumping occurring by intermittently heating the heater ribbon. While this pump arrangement is acceptable in many applications, direct contact between the heater ribbon and the pumped fluid may not be desirable in some medical applications. Such is the case when the pumped fluid has delicate or fragile structure or which is subject to breakdown in the presence of high temperature. In addition, isolation of the heater ribbon and pumped fluid may be necessary to maintain a sterile environment for the pumped fluid.
A pump which solved these and other problems is disclosed in U.S. Pat. No. 4,265,601 which patent is hereby incorporated by reference.
While this improved pump provides accurate pumping for medical applications it was desired to improve the pump to provide a more constant pressure of the pumped fluid at the exit port to reduce the acceleration and deceleration of the pumped fluid thereby decreasing the load requirements on the pump caused by such peaking. Additionally, it was desired to provide an improved bleeding or priming capability so that bubbles could be quickly purged from the valves and various pump and system passageways prior to use.
In order to provide such improved operation, a damping-priming chamber was incorporated which had a substantially larger pumping volume than the pumping chamber but having a similar construction and mode of operation whereby the pressure of a second pumping fluid could be increased to deflect a diaphragm in the priming-damping chamber. The volume of fluid moved on each diaphragm deflection is preferrably greater than the combined volumes of the valves and connecting passageways in the pump apparatus. Thus, utilizing such a priming-damping chamber the pump can be purged of bubbles and can be primed for operation after just one or two cycles or deflections of the diaphragm in the priming-damping chamber. In addition, the remainder of the pumping system including the connecting tubes between the reservoir and the patient can be be quickly purged of air within just a few pumping cycles.
Additionally, the priming-damping chamber provides a pumped fluid sink whereby rapid increases in pressure of the pumped fluid are abated and moderated by the deflection of the diaphragm in the priming-damping chamber. Subsequently, when the pressure of the pumped fluid decreases the diaphragm in the damping-priming chamber begins to return to the non-deflected state, thereby maintaining the pressure of the pumped fluid for an additional period of time. Thus, the pressure of the expelled pump fluid is damped in that it is maintained at a more constant level over a longer period of time without drastic pressure changes in the pumped fluid being expelled. Such drastic changes (i.e., acceleration and deceleration of the pumped fluid) require the pumps to exert a substantially greater force. Therefore, by incorporating the priming-damping chamber, the load requirements on the pump are significantly reduced.